For long slender structures like beams, propping is required after removal of formwork. Why?

After concreting, the time at which striking of formworks should not be too long, otherwise it would affect the colour of concreted structures. For long span concrete structures, when they have attained sufficient strength to support their self-weight, creep deflection may occur in these structures if propping is not provided after the removal of formwork.
Therefore, re-propping is carried out after removing formwork and these props should not be allowed to stand too long because creep loads may overstress them.
Note: Propping refers to provision of falsework to support slabs and beams during their gain in concrete strength after concreting.